Filter cake reinforcement



April .30, 1940.

J. H. FEDELER. JR

FILTER CAKE REINFORCEIIENT Filed April 9, 1958 INVENTOR John H Fade/er, J1.

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A ORNE Patented 'Apr. 30, 1940 PATENT oFFrcE m'raa CAKE aarnro 1.1... n. Fedeler, In, mammals. 1.. animal'- to Tires. 0. Stephens, n. 2.

Application April '9, 1938, Serial No. 201,084 3 Claims. (01. 210-199)..

My present invention relates generally to filters and has particular reference to rotary-drum filters of the general type illustrated and described in United States Patent No. 1,880,005, issued September 27, 1932.

It is a general vide certain improvements in the type of filter in which a series of flexible elements extend around the filter drum, these elements being adapted to become embedded in the filter cake that forms on the drum, thereby serving not only I as a reinforcement for the filter cake but as a convenient means for stripping the cake from the drum and also conveying it along a predetermined path of travel to an ultimate region of discharge.

A filter of the foregoing type has come to be known in the trade as a string-discharge filter,

because the flexible elements are usually com- 2o posed of a series of strings.

is generally of cotton The string that is used or linen or equivalent materials, and preferably of stranded character, 1. e., it is composed of a series of individual strands that are twisted or braided together.

It has been found in practice that the maximum inherent advantages of this type of construction are not always capable of realization,

for various reasons. For example, the employment of a string composed of metal, such as a stranded copper wire, a coiled spring, etc., has usually proved to be impractical. Among other difilculties is the fact that a metallic string has an undesirable abrasive effect upon the screen 35 or mesh that serves as the filtering medium.

Similarly, where a non-metallic string is used, the field of utility is subject to certain limitations. For example, in the filtration of certain slurries, notably those which are markedly alkaline or acid in character, the chemical action has an axis, induces the formation on the string of undemrable fibrous masses known in the trade as fprms'y-ca ,f these being nothing more or less object of my invention to pm.

than a collection of fibers that have wrapped themselves around the string and become entwined with it.

' Another disadvantage of the ordinary non-metallic string lies in the fact that its ends have a tendency to fray, whereby the knot uniting the ends of the string loosens and ultimately becomestulntied within an undesirably short period of It is the general object of the present invention to obviate these and other difliculties heretofore encountered in connection, with a string discharge" filter, thereby widely extending the field of practical utility of this general type of filter.

In seeking to achieve the present objectives, I have found that the mere impregnation of the strings with various protective media is unsuitable toaccomplish the present purposes, because the abrasive action to which the strings are subjected during normal operation of the filter quickly ruptures any protective film that the impregnation may have produced.

In accordance with my present invention, the string is provided with a coating of material which is truly protective in nature. The coating I employ is of impervious flexible material which is resistant to chemicals which. would attack the string itself, and'which is adequately resistant'to -the abrasion to which the flexible reinforcing elements may be subjected either during normal operation of the filter or in the filtering of abra sive products such as those "encountered in the mining field. Moreover, the present coating has a smooth non-fibrous quality which is notsubject to fraying, and which has no tendency topick up and accumulate undesirable masses of fibrous material. Where the string is of metallic character; the present coating serves as a desirable protective sheath which overcomes the difllculties heretofore making metallic strings impractical by themselves.

One of the features of my invention lies in ensheathlng each string in' a protective coating which is bonded to the string. The bonding effect is preferably accomplished by employing a plastic material that is molded into position on the string so that the inner surface of the resultant homogeneous coating conforms snugly to the outer surface of the stranded string. In this way, a staunch unitary reinforcing element is produced,- of adequate flexibility and tensile strength, having ajminimum of stretchability, and admirably manifesting the qualities of resistance to chemical action and'to abrasion which are among themajor objectives of the present invention.

The coating material which I prefer toemploy is vulcanized soft rubber. or its equivalent.

I achieve the foregoing objects, and such other objects as may hereinafter appear or be pointed out, in the manner exemplified in the accompanying drawing, in which- Figure 1 is a fragmentary perspective view, diagrammatic in nature, of a rotatable drum and associated parts of a filter of the present type;

Figure 2 is an enlarged fragmentary view of an illustrative example of one of the present improved flexible reinforcing elements, shown partly in section; and

Figure 3 is an enlarged cross-sectional view taken substantially along the line 33 of Figure 2.

The reference numeral 10 is applied to a drum of a filter of the present type, being rotatable about a shaft or axis H. The details of the drum construction, and of its mounting in a slurry tank, have not been illustrated since these details are known per se and have no direct bearing on the present invention. It will be understood, however, that the drum is mounted to rotate around a substantially horizontal axis with its lower portion immersed in the slurry which is to be filtered. The drum rotates in the direction of the arrow I2, is provided on its surface with a suitable screen or filtering medium, and is usually provided with vacuum producing mechanism and conduits which draw the filtrate inwardly through the surface of the drum, leaving the residue in the form of a filter cake on the drum surface.

Extending around the drum are a plurality of parallel flexible elements l3 adapted to become embedded in the filter cake that is formed, thereby reinforcing the latter and serving as a means to guide the resultant filter cake away from the drum.

Merely by way of example I have shown the flexible elements It traveling tangentially away from the drum l0, around a roller ll of relatively small diameter, thence over a guide roller i5 and back onto the drum I0. During the passage of the elements I: around the roller M, the filter cake breaks away from the flexible elements because of the sharp curvature of travel around the roller l4. During the passage of the flexible elements from the roller H to roller II they are guided between successive prongs or teeth ii of an element I'I, thus serving to keep the flexible elements in proper spaced relationship.

Merely by way of example I have illustrated the present invention in the form it assumes when the flexible element comprises a stranded string l8 (see Figures 2 and 3) ensheathed in a 1 protective coating I9.

I have illustratively shown a string l8 composed of three twisted strands, as shown most clearly in Figure 3, although it will be understood that the string may be composed of fewer or more strands, and that the latter may be twisted or braided or otherwise inter-twined or associated in any suitable or conventional manner.

It will be understood that the string I! may be of the usual cotton or linen variety, or it may be metallic in nature, being composed, for example, of a stranded or braided copper wire, a coiled spring, or the like. In general, it will be understood that the term "string" as used herein and "I in the appended claims is intended tosignify armors this purpose.

It is a particular feature of my invention to apply this sheath in plastic form, preferably under pressure, so that it'is virtually molded into position on the string. This is illustrated clearly in Figures 2 and 3, and attention is drawn to the fact that the'inner surface of the coating ll con-forms snugly to the outer surface of the string. As a result, the coating is bonded to the string not only by virtue of the adhesion that may exist between the string and the coating, but also by the form-fitting relationship between theparts. A unitary flexible element is thus produced, with no relative longitudinal slippage between the sheath and the string. The element has adequate flexibility, it has less stretchability than the string itself, it is resistant to abrasion, and, of considerable importance, it is resistant to chemical action.

The flexible element thus produced has certain other advantages. Its outer surface is-of smooth non-fibrous character so that it has no tendency to ensnare masses of fibrous material; it has no abrasive action upon the filtering medium itself; it has no tendency to fray either at the ends or elsewhere; and it is of a character which permits the core to be of metal or other selected material which might, by itself, be unsuitable for use on a filter.

For these reasons, the improved reinforcing element is admirably adapted to serve in all types of string discharge filters, and is particularly useful where the filter is to be used with alkaline or acid media, e. g., in the filtering and washing of caustic lime mud in the paper industry, in'the filtering and washing of zinc sulphate in the manufacture of paint pigments, and in a large variety of other, arts and industries.

It is to be understood that the use of the present improved reinforcing element is not restricted to a filter in which the flexible elements travel as shown in Figure 1. For example, the discharged reinforced filter cake may be conveyed from the filter drum to a drying drum, or it may be stripped from the reinforcements by means other than the small-diameter roller illustrated merely by way of example in the present In general it will be understood that the de-' tails herein described and illustrated for the purpose of explaining the general nature of the invention, may be modified by those skilled in the art without departing from the spirit and scope of the invention as expressed in the appended claims and that these details are to be interpreted in an illustrative, and not in a limiting sense.

Having thus described my invention and illustrated its use, what I claim as new and desire to secure by Letters Patent is:

1. In a rotary-drum filter, a series of parallel flexible elements extending around the drum and tangentially away from it, said elements being adapted to become embedded in the filter cake that forms on said drum and serving thereby to reinforce the cake and strip it from the drum,

forth in claim 1, said sheath comprising a plastic 7 each element comprising a string ensheathed in a tough homogeneous flexible material having a smooth surface resistant to abrasion and devoid of any tendency to pick up undesirable matter that would ordinarily tend to adhere to the string itself, whereby both the string and the filter parts with which said element comes in contact during the normal operation of the filter are effectively shielded from such undesirable 10 matter.

2. In a rotary-drum filter, the combination set material molded into position on the string so that it is bonded to the string with its inner surface conforming snugly to the outer surface of the string.

3. Ina rotary-drum filter, the combination set forth in claim 1, said sheath comprising vulcanized soft rubber or its equivalent, bonded to the string with its inner surface conforming snugly to the outer surface of the string.

JOHN H. FEDELER, JR. 

